Tyrosine-phosphorylation-dependent translocation of the SLAT protein to the immunological synapse is required for NFAT transcription factor activation.

SWAP-70-like adaptor of T cells (SLAT) is a guanine nucleotide exchange factor for Rho GTPases that regulates the development of T helper 1 (Th1) and Th2 cell inflammatory responses by controlling the Ca(2+)-NFAT signaling pathway. However, the mechanism used by SLAT to regulate these events is unknown. Here, we report that the T cell receptor (TCR)-induced translocation of SLAT to the immunological synapse required Lck-mediated phosphorylation of two tyrosine residues located in an immunoreceptor tyrosine-based activation motif-like sequence but was independent of the SLAT PH domain. This subcellular relocalization was coupled to, and necessary for, activation of the NFAT pathway. Furthermore, membrane targeting of the SLAT Dbl-homology (catalytic) domain was sufficient to trigger TCR-mediated NFAT activation and Th1 and Th2 differentiation in a Cdc42-dependent manner. Therefore, tyrosine-phosphorylation-mediated relocalization of SLAT to the site of antigen recognition is required for SLAT to exert its pivotal role in NFAT-dependent CD4(+) T cell differentiation.

T regulatory cells in autoimmune diabetes: past challenges, future prospects.

INTRODUCTION: Accumulating evidence suggests that defective regulation is an essential underlying cause of autoimmunity. The development of type 1 diabetes in the NOD mouse strain it is a complex process that depends on a fine balance between pathogenic and regulatory pathways. DISCUSSION: We have utilized a series of transgenic and knockout mice to determine the relative importance of regulatory T cells and negative regulatory receptors on the development and progression of type 1 diabetes. CONCLUSION: This review will focus on the origins and function of Treg in peripheral self-tolerance. We will summarize the role of Treg in preventing autoimmune diseases, with a particular focus on Type 1 Diabetes (T1D), and discuss the prospects for Treg-based therapies for autoimmune diseases.

Role for protein kinase Ctheta (PKCtheta) in TCR/CD28-mediated signaling through the canonical but not the non-canonical pathway for NF-kappaB activation.

NF-kappaB is a family of essential transcription factors involved in both embryonic development and inflammatory responses of the immune system. NF-kappaB can be activated by two pathways, i.e. the canonical (NF-kappaB1) pathway, which acts through the catalytic components of the IkappaB kinase complex and leads to IkappaB phosphorylation, degradation, and subsequent NF-kappaB nuclear translocation, or the non-canonical (NF-kappaB2) pathway, which involves NF-kappaB-induced kinase-dependent proteolytic processing of p100/p52 to yield translocation-competent p52-containing NF-kappaB complexes. We examined the relative roles of the NF-kappaB1 and NF-kappaB2 pathways in TCR/CD28 costimulation. We found that TCR/CD28 costimulation activates the canonical but not the non-canonical NF-kappaB pathway and that the serine/threonine kinase protein kinase C (PKC) is essential for TCR/CD28-mediated canonical NF-kappaB activation in T cells. Importantly, TCR/CD28 costimulation induces higher p52 protein levels in T cells, but this effect is secondary to enhanced de novo synthesis of p100, not to enhanced processing of extant p100; PKC deficiency impairs signal-dependent p52 accumulation because of defects in p100 production. Finally, we found that TCR/CD28 costimulation induces IkappaBalpha, IkappaBbeta, and IkappaBepsilon degradation, and PKC is required for IkappaBalpha and IkappaBepsilon but not IkappaBbeta degradation. PKC acts solely within the canonical pathway to activate NF-kappaB, and PKC deficiency impacts upon p100/p52 processing in a manner that is independent of NF-kappaB-induced kinase.

Cutting edge: CD28-mediated transcriptional and posttranscriptional regulation of IL-2 expression are controlled through different signaling pathways.

Despite the clear functional importance of CD28 costimulation, the signaling pathways transduced through CD28 have remained controversial. PI3K was identified early as a candidate for CD28 signaling, but conflicting data during the past decade has left the role of PI3K unresolved. In this report, we have resolved this controversy. We show that mutation of the PI3K interaction site in the cytosolic tail of CD28 site disrupts the ability of CD28 to recruit protein kinase C-theta; to the central supramolecular activation cluster (c-SMAC) region of the immunological synapse, promote NF-kappaB nuclear translocation, and enhance IL-2 gene transcription. In contrast, mutation of the PI3K interaction site had no effect on the ability of CD28 to enhance IL-2 mRNA stability. These results suggest that two distinct pathways mediate CD28-induced up-regulation of IL-2 expression, a PI3K-dependent pathway that may function through the immunological synapse to enhance IL-2 transcription and a PI3K-independent pathway that induces IL-2 mRNA stability.

Perspectives on PKCtheta in T cell activation.

Upon stimulation by environmental signals, T lymphocytes develop an intricate set of signal-dependent responses including remodeling of the actin cytoskeleton, the development of cellular polarity, the initiation of second-messenger cascades, entry into cell cycle, differentiation and effector function. The integration of TCR and costimulatory signaling is critical to the successful initiation of the T cell activation program, and the serine/threonine kinase PKCtheta is an important site of signal integration in the process of T cell activation. We provide an overview of T cell signaling, and then go on to assess our understanding of the regulation of PKCtheta activity, its target proteins and its role in T cell activation and the production of T cell survival factors such as IL-2.

Ordered just so: lipid rafts and lymphocyte function.

Immunologists have long been occupied with the description of cellular activation signaling events that originate with the stimulation of multichain immunoreceptors at the cell surface. These signals are transmitted by a protein-partner-signaling cascade through the cytoplasm to the nucleus, where they culminate in changes in gene expression, metabolic state, and entry into cell cycle. For T cells and B cells, these signaling cascades start with the ligation of the T cell receptor (TCR) and B cell receptor (BCR), respectively, and result in the recruitment and activation of related families of signaling molecules at the cell surface. Until recently, this gathering of signaling proteins was thought to occur within the featureless plasma membrane, a cellular organ that was envisioned as a boundary between the inner and outer components of the cell, but which contributed little to the signaling process. However, the past few years have seen the gradual realization that activation of signaling in lymphocytes takes place in and around specialized membrane subdomains called lipid rafts (also known as DIGs and GEMs). Here, we provide a brief overview of the analogous structures and compositions of lipid raft-associated signaling complexes in T cells and B cells, and the ways in which lymphocytes--and their pathogen adversaries--use lipid rafts to their benefit.